1
general::
Phrase(s): bust a gut
Go to split a gut., Phrase(s): bust a gut (to do something)
Fig. to work very hard; to strain oneself to accomplish something. (The word gut is considered impolite in some circumstances. Bust is a nonstandard form of burst.) • I don’t intend to bust a gut to get there on time. • I busted a gut to get there the last time, and I was the first one there.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, burst a gut. 1. Exert oneself to the utmost. For example, He was busting a gut trying to please her. This hyperbolic term alludes to hurting one's mid-section through physical straining. The first slangy term dates from the early 1900s, the variant from about 1700. For a synonym, see BREAK ONE'S ASS. 2. Explode with strong feeling, especially laughter or anger. For example, Gene almost bust a gut laughing, or The foreman will burst a gut when he learns that the machine isn't repaired. The former dates from the late 1800s, the latter from about 1940.
American Heritage Idioms